The Open Systems Interconnection (OSI) model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar communication functions are grouped into logical layers. A layer serves the layer above it, and is served by the layer below it. At each layer, two entities interact with each other via a specific protocol associated with that layer by transmitting and receiving protocol data units (PDUs). Under the OSI model, seven layers are defined from bottom to top as follows: physical layer (layer 1), data link layer (layer 2), network layer (layer 3), transport layer (layer 4), session layer (layer 5), presentation layer (layer 6), and application layer (layer 7).
The physical layer defines electrical and physical specifications for devices. In particular, it defines the relationship between a device and a transmission medium. The major functions and services performed by the physical layer are: establishment and termination of a connection to a communication medium, participation in the process whereby communication resources are effectively shared among multiple users (e.g., contention resolution and flow control), and modulation or conversion between the representation of digital data in user equipment and the corresponding signals transmitted over a communications channel.
The data link layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the physical layer. The main functions of data link layer include: framing, physical addressing, flow control, error control access control, and media access control (MAC). For local area network (LAN) architecture, which was developed independently of the ISO work in IEEE project 802, the data link layer includes a MAC sub-layer and a media-independent logical link control (LLC) sub-layer. The MAC sublayer manages the interaction of devices with a shared medium, while the LLC sublayer deals with addressing and multiplexing on multi-access media.
In wireless communications systems, wireless devices communicate with each other through various well-defined frame structures. Exchanged bit streams in the physical layer are arranged temporally into sequences called frames. Frames are in turn divided into very specific and standardized sections. For example, the current IEEE 802.11 standards, which specify wireless local area network (WLAN) computer communication protocols in the 2.4, 3.6, 5, and 60 GHz frequency bands, define various frame types for use in transmission of data as well as management and control of wireless links.
In general, a frame comprises sequentially of a PLCP PPDU, a frame header, and a payload. The PLCP PPDU further comprises a preamble, a PPDU header, and a PPDU payload. The PPDU header has one or more signaling fields. Conventionally, a signaling field carries information pertinent to the operation of the physical layer. To decode a frame, the receiver uses the information in the signaling field to determine how to decode the remainder of the frame. The conventional design separates the PHY and MAC layer information by layering them on top of each other and there is no intermingling of the information. For example, each MAC layer frame consists of a MAC header and a MAC payload. The first two bytes of the MAC header form a frame control field specifying the form and function of the frame. Such frame control field must be decoded and then processed in the MAC layer after PHY layer decoding and processing.
To conserve energy, especially for battery powered wireless communications device, it is desired that there is information in the preamble of a frame that facilitates early termination. That is, a receiving wireless device terminates the decoding process earlier. One common approach is to include a full or partial station association identifier (AID) of a wireless communications device into the physical layer header. The Partial AID is a non-unique identifier of a station based on its AID. The wireless communications device stops the decoding process immediately if it finds out that the AID or Partial AID in the receiving frame does not belong to itself. Using AID or partial AID on all type of frames is a generic way to facilitate earlier termination. However, it only provides limited benefit because it does not differentiate frame types defined in wireless communications standards such as null data, control, and management frames for different purposes. A solution to achieve early termination based on frame type is sought.